1. Field of the Invention
This invention relates to hydraulic powered vehicle crash barrier systems, in particular crash vehicle barrier systems having an emergency mode of operation to rapidly raise the crash barrier.
2. Description of Related Art
Vehicle crash barriers are well known for use as anti-terrorism and other security measures. Generally, a crash barrier pivots between a lowered position in which vehicles easily pass over it, and a raised position that prevents passage of vehicles. In order to sustain an impact from a potential vehicular threat, the barriers have substantial mass and are constructed of very heavy gauge steel, and may include concrete.
In order to raise the barrier rapidly, the mechanisms required are typically over-engineered. Examples of mechanisms to raise and lower the barrier based on hydraulics are described, for instance, in U.S. Pat. Nos. 4,850,737, 4,627,763, and 4,490,068, all of which are incorporated by reference herein.
Under normal conditions, rapid deployment of the barrier into its raised position is not necessary. Therefore, hydraulic circuits for barriers have been designed to include a normal-UP mode of operation, a normal-DOWN mode of operation, and an emergency-UP mode of operation. In one example of the system described herein, the normal-UP and normal-DOWN modes of operation, the hydraulic piston raises the barrier typically between about 3 and 5 seconds, and lowers the barrier typically between about 6 and 8 seconds. When a threat is imminent or perceived, the emergency-UP mode of operation is used, enabling the barrier to be raised in about 1 to about 1.5 seconds. For instance, such a system including an emergency-UP mode of operation is described in various product literature and is commercially available from Nasatka Barrier Incorporated of Clinton, Md., USA.
However, problems associated with the hydraulic circuit can result in periods of inoperability of the barrier system. Systems that raise and lower the crash barriers are prone to failure, for instance in the form of hydraulic fluid overpressure that exceed the capacity of various valves, seals or other elements in the fluid pathway.
A hydraulic actuator is generally a sealed cylinder having a pair of variable volume fluid compartments with individual inlet/outlet ports. Under normal operating conditions, hydraulic fluid is pumped from a reservoir into one of the variable volume fluid compartments (a high pressure compartment), thereby displacing the piston and causing the crash barrier to ascend or descend. Hydraulic fluid from the other variable volume fluid compartment (a low pressure compartment) is expelled into the reservoir. However, certain undesirable conditions may cause hydraulic fluid from a high pressure compartment of the hydraulic actuator to leak into the low pressure compartment and into the hydraulic circuit, which will be referred to as an internal leak.
Furthermore, various control valves are in line between the pump and the hydraulic actuator, including a multi-port, multi-position directional control valve (e.g., a sandwich valve) that switches between conduits under control of a solenoid. If the solenoid valve is defective, any resulting overpressure conditions may cause failure in the directional control valve, system hoses, or one or more pressure gauges connected to at various positions in the hydraulic circuit.
In addition, a pressure switch is coupled to a programmable logic controller in order to ascertain the pressurization status of one or more hydraulic fluid lines. The pressure switch is disposed in a hydraulic fluid path between the directional control valve and one of the inlet/outlet ports of the hydraulic actuator (typically the compartment that raises the crash barrier upon increased pressurization due to introduction of hydraulic fluid). This pressure switch is prone to failure, which diminishes control functionality of the programmable logic controller, potentially leading to overpressure conditions that may cause damage to elements in the hydraulic fluid circuit.
If the maximum pressure capacity of any of the system components is exceeded, one or more external leaks can occur, thus wasting hydraulic fluid, potentially creating environmental problems, and, of course, rendering the crash barrier inoperable during the time it takes to make the necessary repairs. If the failure occurs in the raised position, that creates an inconvenience for the normal traffic flow in and out of the facility. If the failure occurs in the lowered position, the facility is left vulnerable to vehicular threats.
Therefore, a need exists for a system and method that overcomes the deficiencies of existing vehicle crash barrier hydraulic circuits.
Accordingly, it is an object of the present invention to provide a pressure relief sub-system that compensates for overpressure conditions in hydraulic circuits that control the vehicle crash barrier.
It is another object of the present invention to provide a pressure relief sub-system that includes an alternate path for pressurized fluid, preventing or minimizing damage to components including the hydraulic actuator, valves, pressure gauges, and other components of the hydraulic system.
It is still another object of the present invention to provide a pressure relief sub-system that recycles hydraulic fluid, even during overpressure conditions.